A Simple Apparatus for Maintaining Low Temperature Temperature is one of the most important parameters, responsible for affecting both physical and chemical processes. Therefore, it l h m a r t e r is required that these processes should take place a t constant temperature. In addition, attaining of different temperatures during temperature-dependent investigation is also desired. Ambient and higher temperatures are normally achieved by employing electrically thermostated hot baths. Similarly, it is fairly w ~ ~ t r ~ ~ easy to use an ice-water bath to maintain 0 "C.However, special and 'nsu'a""g quite expensive temperature controllers are used for obtaining low- sample Tub er temperatures. We propose a simple and inexpensive arrangement EM.,,.^ or I tomaintain low temperatures within small volumes. The apparatus no1 Bdh is shown in the figure below. I t consists of a 30-cm-long and 10-cmdiameter Dewar flask. About one-third of the flask is filled with liquid nitrogen and is covered with a suitably made polystyrene lid. A uniform glass tube of 15 cm length and 5 cm diameter is used as a hath that is filled one-third with a low-freezing-point liquid, ethanol or isopropanol. The tuhe is clamped to an adjustable stand and is suspended in the Dewar flask through the polystyrene lid. I t should be ascertained that there is no "significant"leakage of nitrogen into the atmosphere. The tuhe bath is closed with a rubber cork. The sample tube and a thermometer are dipped into the hath through the rubber cork. A resistance thermometer can be used instead of a glass thermometer. The glass thermometer may function as a stirrer if i t is put directly into the sample tube. The temperature of the bath depends upon the distance between the hath and the level of liquid nitrogen. If the system is well protected against the loss of nitrogen, then no significant change in the level is observed for a period of 2-3 hours. Usually i t takes 15 minutes to attain a constant temperature within the sample. A decrease in the distance between the bath and the level of nitrogen lowers the temperature. When different temperatures are t o he attained, work in the direction of subsequent lowering of temperature in order t o have hetter and quicker results. This apparatus was used todetermine the solubilities of certain liquid samples prior to their low-temperature NMR investigations1-3. The apparatus has provided fairly constant temperatures in the ranee of 265-140 K. We have found that this aooaratus can be of ereat utilitv in teachinelaboratories. I t can also be used in thebiological studies where wntndlcd l
